1. Field of the Invention
The present invention relates to an optical semiconductor module or a photodiode module for use in optical communications or the like and a method for fabrication of the same.
2. Description of the Related Art
FIG. 11 is a sectional view showing an example of a conventional optical semiconductor module. As shown in FIG. 11, reference numeral 1 denotes an optical semiconductor module to which an optical fiber terminal 2 is mounted. The optical semiconductor module 1 comprises a housing 6 and an optical semiconductor element 11, the housing 6 having a ferrule bore 5 acting as an alignment bore for aligning a ferrule 4 holding an optical fiber 3 of the optical fiber terminal 2 and the optical semiconductor element 11 being mounted in a position opposite the ferrule bore 5 to the housing 6 and being sealed by a cap 10 having a lens 9 with a laser chip 7 mounted to a stem 8. The optical semiconductor element 11 is fixed with an adhesive 12 to the housing 6 after the optical axis has been adjusted so as to gather optical outputs into the optical fiber 3 mounted to the ferrule bore 5.
The outputs emitted from the laser chip 7 are gathered through the lens 9 onto the central portion on the bottom surface of the ferrule bore 5 and sent to the optical fiber terminal 2 as given signals.
Conventional optical semiconductor modules generally have the structure as described hereinabove. One critical character which affects the performance of the optical semiconductor modules reside in how a loss in connection with the optical fiber terminal 2 can be reduced by improving the degree of accuracy in fabricating the ferrule bore 5 acting as the alignment bore for aligning the ferrule 4, and by minimizing a gap between the ferrule 4 and the ferrule bore 5 at the time when the ferrule 4 inserted into the ferrule bore 5 of the housing 6, and also how accurately the optical semiconductor element 11 can be fixed to the housing 6 so as to focus the outputs emitted from the laser chip 7 onto the central portion on the bottom surface of the ferrule bore 5. In particular, the structures of the conventional optical semiconductor modules require the ferrule bore 5 of the housing 6 to be fabricated or processed with high accuracy in a cylindrical or circular shape, with no gap or minimal gap existing between the ferrule 4 and the ferrule bore 5. When a single-mode fiber is employed as the optical fiber 3, the diameter of the optical path should be as small as about 10 microns and the accuracy of the ferrule bore 5 should be in the order of less than several microns in terms of each of the tolerance of diameter and circularity. A large number of steps for fabrication is required in order to achieve such a high degree of accuracy. In particular, as the material to be utilized for the housing 6 is generally a metal, mechanical processing is required to fabricate the housing 6. Further, since the diameter of the ferrule 4 is as small as approximately 2.5 mm, and surface roughness must be minute, as resistance to friction upon attachment or detachment of the ferrule 4 is taken into account, productivity is greatly restricted.